Process of thermally decomposing hydrocarbons



Patented Dec. 4, 1934 PATENT OFFICE UNITED STATES PROCESS OF THERMALLY DECOMPOSING HYDROCARBONS Charles J. Strosacker and Harold S. Kendall, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich, a corporation of 1 Michigan No Drawing. Application October 31, 1930. Serial No. 492,618

1 Claim.

The present tween 700 and 1000 0., various types of crackingv retorts may be used, but in general a tubular retort is preferred for facilitating a rapid heatin 1159 of the oil vapors and the maintenance of uniform temperature conditions. In the past the retorts employed for the cracking have been made of iron or steel, including certain special steel alloys such as alloys containing chromium, etc. We have til? now found that a materially greater rate of production of gaseous olefines may be maintained in a retort of any given dimensions and at the same cracking temperature if the heating surfaces of such retort are composed of a nickel-chromium Q5 alloy, or nickel-chromium-iron alloy, in which nickel is the principal constituent. We are aware that it has been proposed in U. S. Patent 1,646,349 to carry out the thermal decomposition of hydrocarbons in contact with an alloy of iron and 83 chromium and also in U. S. Patent 1,703,949 with an iron-chromium alloy containing a minor percentage of nickel. The present invention represents a material advance in the art of crackin hydrocarbon oils over the processes of the aforesaid patents. The invention, then, consists of the steps and means hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail a preferred embodiment of the invention constituting, however, but one of the various ways in which the principle of the invention may be used.

A preferred procedure for carrying out the invention consists in general in vaporizing a hydrocarbon oil, e. g. petroleum or a petroleum distillate such as kerosene, etc., at a temperature preferably below that at which any material cracking thereof to products of lower molecular weight takes place, for instance, between about 300 and 500 C.; passing the vapors under reduced pressure through a retort, preferably a tubular retort, of a nickel-chromium or nickelchromium-iron alloy in which such vapors are contacted with metallic surfaces heated to a temperature between about 700 and 1000 C.; and 55 separating the gaseous products from undecomposed oil vapors. As alloys suitable for the purpose are understood those containing 50 per cent or more of nickel as the principal constituent, to-

' gether with relatively smaller amounts or chromium, with or without iron as a third maj r component. The presence of iron may be a vantageous for practical purposes to lower the cost oi the alloy, improve its mechanical working prop erties or for other reasons. Smaller amounts of other metals may also be present as minor or incidental components, e. g. copper, manganese, etc. In general, suitable alloys are those designated in the trade as Nichrome, the composition of which may vary within the following limits:-

Per cent Nickel 50 to 80 Chromium 10 to Iron 4 to As an example of the improvement realized in practicing the invention, comparative figures are given showing results of cracking kerosene in a tubular retort using tubes of a chrome-nickel iron alloy and of nichrome, respectively. The composition of the chrome-nickel iron alloy was approximately; Cr--18 per cent; Ni-8 per cent, balance chiefly iron: that of the nichrome; Niper cent, Cr-l2 per cent, balance chiefly iron. The tubes were 2 inches in diameter and 6 feet long. The temperature in the crackin zone was held between about 800 and 870 C., and oil was fed at a uniform rate of 11 gallons per hour under an absolute pressure of 5 to 15 inches of mercury. In the table the comparative figures of the average results are shown:--

(Jr-Ni iron Nichrome Per cent kerosene cracked 67. 9 80. 6 Cu. it. gas Brodueed per hour 590 815 Per cent at lene in gas....- 32. 1 31. 1 Per cent big or oleilnes in gas" 32. 4 2& 5 Per cent total olefines in gas 64. 5 69. 6 On. it. ethylene produced per hour 191 254 On. it. total oleflnes produced per hour 384 486 the two diflerent metals, does not imply any limitation upon the conditions for carrying out the cracking operation other than may be specified in the appended claim. In particular the rate of feed of kerosene may be varied if so desired, and we have found that a somewhat higher rate of feed gives further advantages. as shown in the following table, the examples therein having been taken from runs made with the same It is seen that a higher rate of feed results in a slightly reduced percentage of cracking but a higher output of gas and total olefines and a slightly increased percentage of oleiines in the gas.

Other advantages accruing from the use of nichrome tubes or retorts are the resistance to oxidation of the same, which gives increased life in service, and also the very small amount of carbon formation within the tubes. Although a tubular form of retort is preferred, the invention comprehends also the use of other forms of retorts fabricated from nickel-chromium or nickelchromium-iron alloys of the class described, the novelty thereof not being dependent upon the shape, form, nor dimensions of the retort. Likewise it is sumcient to provide a lining of nichrome or equivalent alloy in a retort constructed of iron, steel or other common material, the essential feature of the invention being to conduct the cracking operation in contact with or in the presence of surfaces of nichrome or similar alloy.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the process herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

We therefore particularly point out and distinctly claim as our invention:-

The process of producing olefines which comprises thermally decomposing a hydrocarbon oil at a temperature between 700 and 1000 C. while in contact with surfaces of an alloy containing 50 to per cent nickel, 10 to 25 per cent chromium and 4 to 30 per cent iron.

CHARLES J. S'I'ROSACKER. HAROLD 8. KENDALL Hill 

